The invention pertains generally to the area of image scanning and is more particularly directed to image processing by laser scanning.
The term "optical processing" is used to describe the operations or changes performed on visible electromagnetic radiation (light) containing information (an image) by an optical system. The optical processing of information for various reasons is known in the art and is usually embodied in one of three forms. Either coherent, non-coherent or partially coherent systems are used to process an intelligence into a desired form. A non-coherent optical processing system differs from a coherent or partially coherent system in a number of ways, the main difference being the presence of redundancy. Examples of non-coherent optical processing are noted in an article entitled "Non-coherent Optical Processing" by G. L. Rogers in Optics and Laser Technology" (August 1975), pg. 153-162. Also, in the past many methods for coherent processing of images have been proposed. Some examples of these are described by W. Goodman in "Introduction to Fourier Optics", McGraw-Hill, New York, 1968 at Chapter 7.
Generally, these methods have in common the fact that the original image, which is recorded on a transparency (or reflecting medium) is processed by a coherent (or partially coherent) optical system, and the resulting processed image is in the form of an intensity image that is either displayed or recorded on a recording medium for later viewing or further processing.
For certain applications, it is desirable to obtain an electronic video signal proportional to the irradiance of the processed image. The video signal can be obtained in real time either by scanning the intensity image with a small electrooptic detector or by projecting the intensity image onto a larger transducer such as a TV camera or the like. The first method has very poor light utilization, because the whole image is illuminated by the source and only a very small fraction of the total flux is detected at each instant. In the second method, the quality of the image including its resolution, dynamic range, and a signal-to-noise ratio is limited primarily by the TV camera used. Except for the case of expensive, special-purpose cameras these limitations may be unacceptable.
Recently, there has been developed a scanning system which efficiently uses a collimated source of light in detecting an image to allow the storage and efficient electronic processing of the image. This system, its utilization, advantages, and teachings are more fully described in the cross-referenced copending application, the entire disclosure of which is herein incorporated by reference. The copending application is directed to a method for scanning phase, or surface relief images. However, the method can be practiced equally well with amplitude images such as transparencies and opaque objects. Moreover, in many instances, it is advantageous to combine optical processing techniques on the image information with subsequent electronic processing of the same image information. This may be specifically advantageous when the image parameters to be changed are area changes and do not represent point by point calculations which can be efficiently done electronically.